1. Field of the Invention
The present invention relates to an electrolyte injection apparatus and, more particularly, to an electrolyte injection apparatus for injecting an electrolyte into a case of a battery by using a centrifugal force.
2. Description of the Related Art
Recently, to meet demands for high-performance, large-capacity batteries, various batteries such as alkaline secondary batteries and lithium ion secondary batteries have been developed and put into practical use. Alkaline secondary batteries are widely used because they can be manufactured at a lower cost, have a higher safety, and can discharge with a larger current than lithium ion secondary batteries. A nickel-cadmium secondary battery as one example of an alkaline secondary battery is manufactured by the following method. First, an electrode group is formed by winding a laminated structure obtained by interposing a separator consisting of polyamide fiber unwoven fabric between a positive electrode containing nickel hydroxide and a negative electrode containing cadmium oxide. This electrode group is accommodated in a cylindrical case, and an alkaline electrolyte is injected into the case. Thereafter, the opening portion of the case is sealed to complete a secondary battery. The alkaline electrolyte must be injected into the case with a high accuracy in respect of the cell performance.
Jpn. Pat. Appln. KOKAI Publication No. 59-134558 has disclosed an apparatus for injecting an alkaline electrolyte into the nickel-cadmium secondary battery which contains no electrolyte. This injection apparatus comprises two funnels, two supporting means for supporting the funnels respectively, and two holding means each for holding a case accommodating an electrode group. Each of the cases is located below one of the funnels. Each funnel having an exit hole is inserted into the opening portion of the corresponding case such that the exit hole is closed with the upper end of the electrode group. Each of the supporting means and each of the case holding means are suspended from both sides of a rotary bar.
In this apparatus, each case accommodating the electrode group is connected to the corresponding holding means, each of the funnel is connected to the corresponding supporting means. A predetermined amount of an alkaline electrolyte is supplied to both funnels. Subsequently, the rotary bar is rotated. By this rotation, a centrifugal force acts on each of the holding means, which assumes a horizontal position. Then, the electrolyte in the funnels is accelerated to the exit hole by the centrifugal force, and readily flows into the case. Consequently, the electrolyte is absorbed by the electrode group in the case.
A nickel-metal hydride secondary battery as another example of an alkaline secondary battery comprises a cylindrical case. An electrode group is housed in the case. The electrode group is made of a laminated structure obtained by interposing a separator consisting of, e.g., polyamide fiber unwoven fabric between a positive electrode containing, e.g., nickel hydroxide as an active substance and a negative electrode containing, e.g., a hydrogen-absorbing alloy as an active substance. The electrode group is formed, for example by spirally winding this laminated structure. An alkaline electrolyte is also contained in the case. It is considered that the electrolyte is injected into the case by using the above apparatus. However, when the case accommodating the electrode group with the above construction is incorporated into the apparatus and the exit hole of the funnel of the apparatus is closed with the upper end of the electrode group, the exit hole of the funnel is clogged up by the separator, and this makes it difficult to inject an alkaline electrolyte into the case.